一种高压输电线路故障暂态分量自由振荡主频率的估算方法

A Method to Estimate Main Frequency of Free Oscillation in Fault Transient Component of UHV Transmission Line

由于高压远距离输电线路分布电容很大,故障后产生的自由振荡频率分量不可忽略。在自由振荡频率分量中最接近于工频分量的称为自由振荡主频分量。针对自由振荡主频分量,以往的分析方法仅利用经过反复验证才能应用的推论进行推导,缺乏普遍意义,并且推导得出的衰减时间常数并不准确。针对此问题,基于继电保护中经常采用的假设"系统元件阻抗角相等",提出一种新的暂态分量分析方法,推导出高压输电线路自由振荡主频的表达式以及主频范围,简便、清晰地估算出自由振荡主频率的大小,验证自由振荡主频率存在于一定范围内,实现了对主要暂态分量的理论分析,为其在继电保护方面的应用提供理论基础。新方法推导得到的衰减时间常数更加准确。并且,文中还将这种新的推导方法应用于接入并联电抗器等场合的暂态分析中。最后利用PSCAD对特高压线路模型进行仿真,仿真结果证明了新分析方法的正确性。

Due to its large distributed capacitance the post-fault frequency components of free oscillation in UHV transmission line cannot be neglected.In these frequency components the one,whose oscillation frequency is most close to fundamental frequency,is called main frequency component of free oscillation.For main frequency component of free oscillation,in bygone analysis methods the inference,which is repeatedly verified,is utilized to derive the main frequency component of free oscillation,so the derived result of such a method lacks of universal significance and the derived time-constant is inaccurate.To solve this problem,based on the hypothesis widely adopted in relay protection,i.e.,the impedance angles of system elements are equal,a new method to analyze transient components is proposed,and the expression for main frequency of free oscillation of UHV transmission line as well as the range of the main frequency are derived,therefore the main frequency of free oscillation can be estimated simply and clearly and it is verified that the main frequency of free oscillation exists in a certain range,thus theoretical analysis on main transient components is implemented and theoretical basis for applying it in relay protection is provided.Results of PSCAD-based simulation show that the proposed method is correct.The proposed method is applied in transient analysis of such circumstance as parallel reactor is connected to transmission line and so on,and the decay constant derived by the proposed method is more accurate.